1. Field of the Invention
The present invention relates to an organic solid state optical "and/or" gate and a method for producing an organic solid state optical "and/or" gate, and specifically an organic solid state optical switch containing a plurality of excited states in selected combinations which may be switched by a plurality of light signals or a combination of light signals and a method for producing said organic solid state optical switch containing a plurality of excited states.
2. Background of the Invention
Basic functions of a computer include information processing and storage. In von Neumann (serial) architectures, those arithmetic, logic, and memory operations are performed by devices that are capable of reversibly switching between two states often referred to as "0" and "1." Semiconducting devices that perform these various functions must be capable of switching between two states at a very high speed using minimum amounts of electrical energy in order to allow the computer to perform basic operations. Transistors perform the basic switching functions in computers.
While the design and production of energy-efficient, state-of-the-art electronic devices depend increasingly on the ability to produce ever higher densities of circuit elements within integrated circuits, semiconductor-based computer technology and architecture have advanced to nearly the quantum mechanical limitations of such configurations. Soon, size and price will limit the use of high-performance computers. The major component that modulates these attributes of high-performance computers is the memory.
Because of the huge data storage requirements of these instruments, a new, compact, low-cost, very high capacity, high speed memory configuration is needed. To reach this objective, molecular electronic switches, wires, microsensors for chemical analysis, and opto-electronic components for use in optical computing are being pursued. The principal advantages of using molecules in these applications are high component density (upwards of 10.sup.18 bits per square centimeter), increased response speeds, and high energy efficiency. If light is used to control molecular devices, many of the quantum statistical problems associated with high packing would be outweighed by pico-second (ps, 1 pico-second=10.sup.-12 seconds) response times, which are the typical time lapses observed for switching time and relaxation of the predetermined organic material.
Optical transistors, used in the field of molecular optics, perform the same operations as their electronic analogs, but instead of controlling an electrical signal, the optical transistor modulates light. An advantage of all-optical inorganic or organic devices is the elimination of electromagnetic interference or crosstalk that often plagues electronic devices in tightly packed circuits. However, many ionic crystalline materials are more likely to become damaged with laser exposure than are their organic counterparts. The higher resilience of organic materials can be attributed to the high degree of cross-linking found within said complexes. In addition, many organics are more transparent than inorganic optical materials at certain frequencies. An advantage of incorporating organics into optical switches is that the wavelength dependence of transparency of a device can be controlled by synthetic design to match specific laser frequencies.
Optical effects presently developed using organic materials are due to the interaction of light with solutions. Solvent systems are often needed, as in some instances, a particular molecule is not individually switchable in solid state. This solvent effect results from solvent dipoles reorientating around an ion pair in a polar liquid, thereby decreasing the energy of the ion pair, which obviously differs from the situation in solid state wherein solvent dipoles cannot reorient around an ion pair produced. This lack of reorientation produces an energy level of the ion pair that is much higher in rigid matrices than in liquid, so high in fact that the energy requirement lies above the energy of the excited state, in which case photoinduced electron transfer cannot occur.
Disadvantages with solution systems include the presence of solvent interactions and the need for complex device structures. The threshold energies driving these configurations will not suffice in applications requiring solid state switching, as solid state switching requires approximately 0.8 eV (20 kcal) of additional energy compared to solution systems.
Single crystals, polycrystalline films, and amorphous compositions are potential solid state alternatives to solution systems. (See e.g. U.S. Pat. Nos. 4,574,366 and 4,731,756.) However, some of these systems require that heat energy be applied to change illuminated areas from the second state back to the first state. Furthermore, many of the molecular switches heretofore produced have been restricted in use to non-solid state, polar solutions, primarily due to energy limitations.
Other previous attempts to produce chemical switches have yielded switches which manifest a photochromic change concomitant with a change in molecular structure. For example, such photochromic compounds as spiropyrans and aberchrome dyes, each of which have a plurality of stable isomers which exhibit different absorption maxima, have applications in reversible optical memory configurations. These embodiments exhibit relatively slow switching times ranging from millisecond to microsecond durations. As such, photochromic molecules that are based on reversible electron transfer reactions for optical switching should have advantages in both speed and photostability over molecular switches based on photochemical changes in molecular structure.
Other molecular electronic devices, such as that disclosed in U.S. Pat. No. 5,063,417, utilize a chain of electron transfer molecules wherein the information is shifted down a polymer string by photoinduced electron transfer reactions. However, such configurations suffer from not being able to "reset" the initial electron donating moiety from within the compound structure and appear to handle only one electron transfer at a time. Furthermore, the quinones used in such molecular electronic devices are susceptible to irreversible reduction if hydrogen ions are present, thereby not providing the gate function featured in the present invention.
Optical devices based on organic single crystals and polymers exhibit a variety of potentially important optical processes, including but not limited to the following:
Optical bistability, PA1 Optical threshold switching, PA1 Photoconductivity, PA1 harmonic generation, PA1 optical parametric oscillation, and PA1 electro-optic modulation.
In many organic materials, the optical performance and efficiency equals, and in many cases surpasses, that of the best ionic crystalline inorganic materials. The diversity of organic materials also offers greater ease of fabrication and low cost. Organic compounds and polymers allow for control of optical properties of the device by altering the organic molecular structure before beginning the fabrication process. This "molecular architecture" feature simplifies the manufacturing process compared to silicon technologies by reducing the number of device fabrication steps and by locking the optical properties of the device into the molecular structure itself instead of in the processing techniques.
A need exists in the art to produce an organic system to serve as a cornerstone for a "real time" threshold logic element based on the excited state photophysical properties of said organic systems. These chemical switches should be operational in solid states. Such a system must feature high quantum efficiency of photosynthetic charge separation. This high efficiency depends on favorable electron-transfer rates between electron donors and acceptors that are positioned in precise spatial relationships relative to one another and that possess redox potentials which result in movement of an electron down a stepped potential gradient. Other criteria of such an organic molecule system include optical responsivity at common laser wavelengths, low optical threshold powers and processability into device structures.